The use of filters in communication systems can be essential as they remove unwanted frequency components from a signal. Their selectivity (which is a measure of how well unwanted frequency components are suppressed) and linearity (which is a measure of the amount of frequency components introduced by the filter itself) strongly influence the design requirements for subsequent blocks in the systems, and affect both the performance and power consumption of the communication device. Designing filters using small, cheap active components, instead of bulky inductors, allows for monolithic integration. Because of their active nature, those filters, however, consume energy, have limited linearity, and generate noise.
Source-follower based filters as illustrated in FIG. 1 and discussed further in the detailed description have been proposed in the art. Because of their inherent feedback mechanism, the source follower based filters consume less power. However, because the poles and zeroes in the transfer function of the filter cannot be placed independently from each other, designing a filter with good selectivity may require cascading numerous filter stages. This limits the filter linearity and noise performance, and increases its power consumption. In other words, filter design can be challenging due to the observed trade-off between power consumption, on the one hand, and linearity and noise, on the other hand.
The problem that the applicant tries to solve, and which is at the origin of the instant disclosure, is to provide a filter with good linearity, good selectivity, and low power consumption which are suitable for monolithic integration.